This invention relates to an acceleration slip control device for a wheeled vehicle, which counteracts the acceleration slip occurring at the driving wheels of a wheeled vehicle on an incipient driving moment or in driving. More particularly, the device presented herein controls the extent of opening or closing of a throttle valve in order to control the output torque of an internal combustion engine thereby enabling restraint of the acceleration slip.
Conventionally, slip of the driving wheels, which is caused by the urgent acceleration on a starting moment or in driving of the vehicle, produces several undesirable results. It not only worsens tire abrasions but also deteriorates driving performance due to a decreasing lateral drag force existing in the contact of the tires and the road surface, and moreover wastefully increases fuel consumption.
Previous attempts have been made at overcoming or counteracting the aforementioned undesirable results. For instance, some other inventions were disclosed to restrain the acceleration slip, notably the Japanese Applications Nos. Sho 60-130585 and 60-147277. In these applications, the deviation between the rotational speed of the driving wheels and the running speed of the vehicle is indicative of the slip condition, according to which the throttle valve angle is controlled to the proper extent and output torque can be thus restrained. Adjustment of the throttle valve angle controls the output torque of the internal combustion engine, so that the acceleration step occurring during the vehicle's acceleration could be restrained and the desired slip ratio could be accomplished at that moment.
As has been known, as the throttle valve angle changes, the rate and degree of change of the output torque of the internal combustion engine varies significantly as a function of the driving condition of the internal combustion engine. The driving condition of the internal combustion engine can be affected by the rotational speed of the engine, a negative pressure in an intake passage and so on. FIG. 7 graphically illustrates such a relationship wherein the determination of the output torque varies with respect to the engine speed as the throttle valve angle gets smaller. Therefore, in the inventions disclosed in the Japanese applications, the control quantity on the throttle valve operation is determined in connection with the operational condition of the internal combustion engine, producing the maximum torque deterioration for the minimum throttle valve angle displacement. The utput torque is thus modified to the most adequate extent, avoiding excessive torque modification such as to extremely lower the rotational speed of the driving wheels, or to sometimes reproduce the slip.
Accordingly, the acceleration slip controllers previously known could set the proper output torque under the driving condition, where the output torque abruptly decreases as the throttle valve angle is modified to be even slightly smaller, so that the output torque could be properly restrained to counteract the acceleration slip. Nevertheless as a matter of fact, under some other conditions, namely under the condition where the output torque deteriorates very gradually as the throttle valve angle is modified to be smaller, the operation thereof results in dull responsiveness of output torque restraint. It is obviously seen by the graph of FIG. 7, wherein an equal change in valve angle may result in either an effificient restraint as in the lower half of the graph, or an insensible degree of deterioration as in the upper portion of the graph. Because the conventional controller usually determines the throttle valve angle modificationn in the same manner as during the former driving condition, there is insufficient control quantity for the valve angle in the latter condition and the output torque is not effectively restrained.
As described hereinbefore in the prior art acceleration slip controllers, the variation in degree and rate of change of the output torque deterioration with respect to the throttle valve angle has not yet been designated and moreover the control quantity of the throttle valve is determined only on the basis of the slip condition of the driving wheels. In other words, in previously known arrangements, the control of virtual output torque does not sufficiently compensate for the variation in degree and rate of change in the output torque resulting from the various driving conditions of the internal combustion engine. Hence, the output torque cannot be regularly restrained to the proper extent, even when the slip on the wheels occasionally occurs in the same condition, while the internal combustion engine runs in different speeds.